The present invention relates to a method and device for reducing the percentage of hydrogen peroxide in gas exhausting from a sterilization chamber containing hydrogen peroxide vapor.
A very common method for sterilizing medical instruments and devices comprises contacting the instruments and devices with vapor phase hydrogen peroxide. Several systems are available commercially to effect such sterilization, such as the STERRAD(copyright) Sterilization Systems available from Advanced Sterilization Products division of Johnson and Johnson Medical of Irvine, Calif. In general, such sterilization systems comprise a chamber into which the instruments to be sterilized are placed. Air within the chamber is evacuated and hydrogen peroxide in the vapor phase is admitted to the chamber. Some systems, such as the STERRAD(copyright), additionally induce a plasma upon the hydrogen peroxide sterilization gases. This enhances the sterilization and has the added benefit of disassociating the hydrogen peroxide molecules such that when the hydrogen peroxide plasma returns to its gaseous state, the molecules recombine to form simple oxygen and water vapor thereby lessening the need to deactivate the hydrogen peroxide before exhausting it from the sterilization chamber into the-environment.
Some systems forego the plasma and merely rely upon the hydrogen peroxide vapor to effect sterilization. A common practice for such systems, is to vent their exhaust to a vent exterior of the room housing the sterilizer, typically to a vent pipe on the roof. Little or no attempt is made to chemically alter the hydrogen peroxide and it leaves the vent in active form. A drain may be provided to collect any liquid hydrogen peroxide. Such a venting system inhibits movement of the sterilizer making it impractical to move between laboratories etc. as the vent requires the sterilizer to remain at a fixed location.
Even with most or all of the hydrogen peroxide being broken down by induction of a plasma, it is desirable to provide some means to deactivate hydrogen peroxide. For instance, the admission of hydrogen peroxide raises the pressure within the chamber and it is often desirable to further evacuate the chamber to lower the pressure. The evacuated gasses will thus contain a concentration of hydrogen peroxide. The STERRAD(copyright) sterilization system currently available employs a filter comprising copper wool over which gases being exhausted from the chamber are passed. Copper is a well-known catalyst for hydrogen peroxide, although a rather inefficient one. The contact between the hydrogen peroxide and the copper wool tends to break down at least a portion of any hydrogen peroxide exhausting from the chamber into water and oxygen.
Applicants have developed an improved method and devices for reducing hydrogen peroxide emissions from such a sterilization chamber.
A method, according to the present invention, is provided for cleaning gas exhausting from a chamber which contains a chamber gas comprising hydrogen peroxide. Gas exhausting from the chamber passes along a flow path from the chamber to an exit port. A bed of members coated with a precious metal catalyst for hydrogen peroxide is disposed within the flow path and the exhaust gas passes over the members and catalytically reacts therewith to convert the hydrogen peroxide to water and oxygen. Thus, the exhaust gas reaching the exit has a substantially reduced amount of hydrogen peroxide compared to the chamber gas. Preferably, the precious metal catalyst is selected from the group consisting of palladium, platinum, rubidium and compounds and alloys thereof.
Preferably, a vacuum pump is used to exhaust gas from the chamber. The bed may be located between the vacuum pump and the exit. If so, the members are preferably comprised of alumina, and more preferably the coating of precious metal catalyst on the members is sufficiently discontinuous to allow lubricating oil entrained within the exhaust gases to be absorbed into the alumina members whereby the amount of any such entrained lubricating oil available to deposit upon the catalyst and reduce an available surface area thereof is reduced. These members are preferably substantially spherical, although ovoid or other smooth shapes are desirable. When located downstream of the vacuum pump undue turbulence of the flow may enhance distribution of any entrained lubricating oil from the pump and hasten poisoning of the catalyst. A mass of metal wool disposed within the flow path upstream and adjacent the bed entraps within the wool oil entrained in the exhaust gas and diffuses the exhaust gas to enhance its distribution through the bed. Further, a portion of the bed adjacent the wool can be provided with alumina or other oil absorbent members without the precious metal coating to absorb entrained oil before it reaches the catalyst.
The bed can also be disposed between the chamber and the vacuum pump. The members may be provided with bores therethrough so that the exhaust gas flows through the bores to induce and enhance turbulence thereby enhancing the catalytic reaction. Preferably, such members are tubular. These members may be formed of a polymer such as polyethylene with the catalyst thereon.
A converter, according to the present invention, for cleaning gas exhausting from a chamber comprises a casing having a gas flow path therethrough, the flow path extending to an exit port on the casing. A connector on the casing connects to the chamber whereby gas exhausting from the chamber flows through the flow path. A bed of members coated with a precious metal catalyst for hydrogen peroxide is disposed within the flow path whereby hydrogen peroxide in gas exhausting from the chamber catalytically reacts with the catalyst to convert the hydrogen peroxide to water and oxygen.